Carcinogens in the environment

DEFINITION: Substances or physical agents that cause or worsen cancer

The effects of human exposure to carcinogens in the environment may include the development of different types of illnesses, deaths, and economic obligations on a national and global scale.

Cancer is a leading cause of death throughout the world. Environmentalists and others have raised concerns regarding the cancer-causing (carcinogenic) potential of exposure to a constantly growing number of both newly developed and long-existing chemicals in the environment. In addition, humans are increasingly exposed to various sources of electromagnetic waves, such as microwaves and radiofrequency waves, and some individuals have expressed concern about the potential carcinogenicity of these physical phenomena. However, regulatory authorities have not classified these exposures as a concern.

Carcinogens can be categorized based on their origin as chemicals (naturally occurring or synthetic), physical agents, or infectious agents. Chemical carcinogens can be classed as compounds that occur naturally, such as aflatoxins, chromium 6 compounds, and arsenic compounds; and others that are largely synthetic in origin, such as benzene, formaldehyde, vinyl chloride, and dioxins. In addition, there are carcinogenic minerals, such as asbestos. Other carcinogenic chemicals are elements or substances such as radon (a radioactive gas), beryllium, and cadmium. Some carcinogens—such as tobacco smoke and alcoholic beverages—are mixtures of compounds. Physical agents that are carcinogens include solar radiation (primarily ultraviolet radiation), gamma rays, and X-rays.

Infectious disease agents that have been implicated as carcinogens include human papilloma virus (HPV), which can cause cervical cancer; Helicobacter pylori (H. pylori), a bacterium causally associated with stomach cancer; the hepatitis C and hepatitis B viruses, which can cause liver cancer; Epstein-Barr virus, which is associated with Burkitt’s lymphoma; and human T-lymphotrophic virus type 1 (HTLV-1), which has been linked to leukemia in adults. The human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), has been associated with Kaposi’s sarcoma. Viruses have also been shown to cause tumors in animals such as mice (mammary tumor virus), chickens (Rous sarcoma virus), and Tasmanian devils.

Exposure to carcinogens can be related to work environments, such as in the case of workers in the nuclear power and medical radioisotope industries. Sometimes carcinogenic agents are concentrated in particular geographic regions; for example, widespread exposure to the carcinogen arsenic occurred in Bangladesh due to contaminated drinking water from a large number of wells that accessed groundwater with unusually high arsenic levels. Exposure to H. pylori is believed to occur through contaminated water supplies and is therefore considered to be of environmental origin. Tobacco smoke, a major cause of lung cancer, is an environmental carcinogen to which people are widely exposed.

Carcinogens may lead to cancer by directly damaging deoxyribonucleic acid (DNA), as in the case of radiation; through conversion through metabolism; or through effects on metabolism. In the case of viruses, viral genetic material may be incorporated into host DNA at sites of oncogenes, which are genes whose altered function or disruption leads to cancer. Different carcinogens often lead to effects on different organs, thus H. pylori is associated mainly with stomach cancer, whereas tobacco smoking or use is associated with lung, oral, and laryngeal cancers (and also bladder, colon, and kidney cancers, among others), and asbestos is primarily linked to lung cancer. The time and frequency of exposure to carcinogens, as well as a person’s genetic background, can also influence the likelihood that a carcinogen causes cancer.

Bibliography

"Cancer-Causing Substances in the Environment ." National Cancer Institute, 17 June 2022, www.cancer.gov/about-cancer/causes-prevention/risk/substances. Accessed 24 Sept. 2025.

"Cigarette Smoking: Health Risks and How to Quit." National Cancer Institute, 23 Oct. 2023, www.cancer.gov/about-cancer/causes-prevention/risk/tobacco/quit-smoking-pdq. Accessed 24 Sept. 2025.

"EPA Efforts to Reduce Exposure to Carcinogens and Prevent Cancer." US Environmental Protection Agency (EPA), 3 May 2024, www.epa.gov/environmental-topics/epa-efforts-reduce-exposure-carcinogens-and-prevent-cancer. Accessed 15 July 2024.

"15th Report on Carcinogens ." US Dept. of Health and Human Services, National Toxicology Program, 23 Apr. 2025, ntp.niehs.nih.gov/research/assessments/cancer/roc. Accessed 19 Sept. 2025.

Hill, Marquita K. “Chemical Exposures and Risk Assessment.” Understanding Environmental Pollution. 4th ed., Cambridge UP, 2020.

"Known and Probable Human Carcinogens." American Cancer Society, 1 Aug. 2025, www.cancer.org/cancer/risk-prevention/understanding-cancer-risk/known-and-probable-human-carcinogens.html. Accessed 19 Sept. 2025.

McKinnell, Robert. G., et al. The Biological Basis of Cancer. 2nd ed., Cambridge UP, 2006.

Ward, Elizabeth M. “Cancer.” Occupational and Environmental Health: Recognizing and Preventing Disease and Injury. Edited by Barry S. Levy, et al., 6th ed., Lippincott, 2011.